Adding compress/decompress script for use with gfx

menu/decompress.py

@@ -0,0 +1,112 @@
+import sys
+
+def decompress(compressed_data):
+    out = bytearray()
+    i = 0
+    
+    while i < len(compressed_data):
+        cmd = compressed_data[i]
+        
+        if cmd == 0xFF:
+            # End marker
+            break
+        
+        i += 1
+        
+        # Decode based on top 3 bits
+        top_bits = cmd & 0xE0
+        
+        if cmd < 0xE0:
+            # Standard commands
+            length = (cmd & 0x1F) + 1
+            
+            if top_bits == 0x00:
+                # Raw copy
+                out.extend(compressed_data[i:i+length])
+                i += length
+            elif top_bits == 0x20:
+                # Repeating byte
+                byte_val = compressed_data[i]
+                out.extend([byte_val] * length)
+                i += 1
+            elif top_bits == 0x40:
+                # Repeating word - alternates between two bytes
+                byte_a = compressed_data[i]
+                byte_b = compressed_data[i+1]
+                for j in range(length):
+                    if j % 2 == 0:
+                        out.append(byte_a)
+                    else:
+                        out.append(byte_b)
+                i += 2
+            elif top_bits == 0x60:
+                # Incremental
+                start_val = compressed_data[i]
+                for j in range(length):
+                    out.append((start_val + j) & 0xFF)
+                i += 1
+            elif top_bits >= 0x80:
+                # Copy from past (absolute offset)
+                offset = compressed_data[i] | (compressed_data[i+1] << 8)
+                for j in range(length):
+                    out.append(out[offset + j])
+                i += 2
+        else:
+            # Extended command (0xE0-0xFE)
+            # Command type from bits 5-7 (after shifting)
+            cmd_type = ((cmd << 3) & 0xE0)
+            # Length from bits 0-1 of command (high) + next byte (low)
+            length_high = cmd & 0x03
+            length_low = compressed_data[i]
+            length = (length_high << 8) | length_low
+            length += 1
+            i += 1
+            
+            if cmd_type == 0x00:
+                # Extended raw copy
+                out.extend(compressed_data[i:i+length])
+                i += length
+            elif cmd_type == 0x20:
+                # Extended repeating byte
+                byte_val = compressed_data[i]
+                out.extend([byte_val] * length)
+                i += 1
+            elif cmd_type == 0x40:
+                # Extended repeating word - alternates between two bytes
+                byte_a = compressed_data[i]
+                byte_b = compressed_data[i+1]
+                for j in range(length):
+                    if j % 2 == 0:
+                        out.append(byte_a)
+                    else:
+                        out.append(byte_b)
+                i += 2
+            elif cmd_type == 0x60:
+                # Extended incremental
+                start_val = compressed_data[i]
+                for j in range(length):
+                    out.append((start_val + j) & 0xFF)
+                i += 1
+            elif cmd_type >= 0x80:
+                # Extended copy from past
+                offset = compressed_data[i] | (compressed_data[i+1] << 8)
+                for j in range(length):
+                    out.append(out[offset + j])
+                i += 2
+    
+    return out
+
+if __name__ == '__main__':
+    if len(sys.argv) != 3:
+        print("Usage: python decompress.py <input_file> <output_file>")
+        sys.exit(1)
+    
+    with open(sys.argv[1], 'rb') as f:
+        compressed = f.read()
+    
+    decompressed = decompress(compressed)
+    
+    with open(sys.argv[2], 'wb') as f:
+        f.write(decompressed)
+    
+    print(f"Decompressed {len(compressed)} bytes to {len(decompressed)} bytes")